1. Field of the Invention
The present invention relates to a motorcycle's rearview mirror support structure. More particularly, the present invention relates to a vibration dampening device of the support structure for dampening vibrations of the rearview mirror.
2. Description of Background Art
Support structures for a motorcycle's rearview mirror which include a vibration dampening device are known. For example, Laid-open Japanese Patent No. Sho 59-106740, titled "Vibration Isolating Mirror," and Laid-open Japanese Patent No. Sho 61-203180, titled "Structure Attaching a Rearview Mirror to a Motor-Cycle" describe rearview mirror support structures which include a vibration dampening device. For purposes of an introduction to the background art, the two Japanese Patents will be briefly described.
Japanese Patent No. Sho 59-106740 shows a rearview mirror 14 and a supporting structure. The rearview mirror includes a vibration dampening device in the form of an isolated weight 28 attached through a couple of elastic members 26 and 27 to a mirror backing 24. The isolated weight 28 is contained inside a mirror housing 21.
The dampening efficiency of the vibration dampening device is directly related to the size of the isolated weight 28. Therefore, if vibrations are to be adequately dampened, the size of the mirror housing 21 must be made large enough to accommodate a relatively large isolated eight 28. Often, it is desirable to make the mirror housing 21 small in order to maintain a sleek appearance of the motorcycle, and to improve the aerodynamics of the motorcycle. However, a small mirror housing 21 has insufficient space to house an adequately sized isolated weight 28. Thus, the isolated weight 28 must also be reduced in size, and the vibration dampening performance correspondingly suffers.
Japanese Patent No. Sho 61-203180 shows a rearview mirror 5. The rearview mirror 5 is connected to a mirror stay 8. A bolt 16 connects the mirror stay 8 to a fairing stay 9. The bolt 16 is connected to the mirror stay 8 through a vibration dampening device 12.
The vibration dampening device 12 includes an inner collar 13, an outer collar 14 and a rubber member 15 sandwiched between the inner collar 13 and the outer collar 14. The vibration dampening device 12 is designed to reduce the amount of vibration in the rearview mirror 5 by reducing vibrations in the mirror stay 8.
In a structure for supporting a rearview mirror of a motorcycle wherein the rearview mirror is attached to the fairing stay, two types of vibrations must be accommodated. The rearview mirror itself will tend to vibrate due to its own resonance, and vibration will tend to propagate from the fairing stay to the rearview mirror. The vibrations in the fairing stay may be due to engine vibrations and suspension vibrations as the motorcycle is operated.
Japanese Patent No. Sho 61-203180 discloses that in order to suppress the respective forms of vibration, that the volume of the vibration dampening device 12 should be increased, and that the stiffness of the fairing stay 9 should be increased.
As drawbacks to these disclosed solutions, if the volume of the vibration dampening device 12 is increased, the base of the mirror stay 8 must be increased. Again, it is often desirable to maintain a thin mirror stay for the purposes of sleek appearance and aerodynamics. Further, if the stiffness of the fairing stay 9 is increased, the total weight of the motorcycle correspondingly increases, giving rise to decreased performance of the motorcycle.